The present invention generally relates to filters of the type used in cooking environments to remove grease, oil and other particulates from the air. More particular, the invention relates to a filter unit and method for filtering grease, oil and particulates from hot fumes and transferring heat from the hot fumes to a fluid circulating within the unit. The heated fluid may then be used to supply heat for purposes such as heating water or air.
During the operation of commercial or institutional kitchens, a significant amount of valuable heat energy is lost as a result of hot fumes and/or air being vented to the atmosphere. These hot fumes are generated from cook stoves, hot plates, deep fat fryers, and other cooking apparatus. As a result of such extreme heat and variety of particulates generated during cooking, it is necessary for the comfort and health of kitchen workers to exhaust these fumes, usually on a continuous basis, through flue chimneys or similar venting devices. This process effectively replaces the hot kitchen air with cooler, clean outside air. Although this circulation process is necessary to provide a constant source of clean air to the kitchen environment, this venting practice is both inefficient and uneconomical, especially in colder climates where the cost to heat internal air and water is significant.
A further problem encountered in commercial kitchens is the filtering of grease, oil and other particulates entrained in the hot fumes generated during the cooking of foods. If improperly filtered, entrained grease, oil and particulates can cause fouling and the eventual malfunction of air ventilation systems, as well as create fire hazards if allowed to accumulate. Accordingly, hot fume air filters, which are normally located in fume hoods over cooking surfaces, are generally required to be cleaned daily or at a minimum several times a week. This tedious cleaning process is both time consuming and expensive.
The use of heat exchangers to capture thermal energy above cooking surfaces has been known for years. These designs, however, position the heat exchangers substantially downstream of existing filtration units intended to filter grease, oil and other particulates. This approach is unfavorable for a number of reasons. First, these designs are inefficient since the heat exchanger is located downstream of the filtration unit and a significant distance from the heat source. Thus, valuable thermal energy is lost by absorption into the filtration unit and through general dissipation prior to the heat reaching the exchanger. Second, conventional grease filtration units can significantly impede air flow, especially when congested with grease and oil, hence reducing the efficiency of the air ventilation system and the efficiency of a heat exchanger downstream of the filtration unit. Third, when the heat source is turned off, grease quickly solidifies on filters and heat exchange, and must be removed for both safety and efficiency. Finally, despite the existence of these types of heat exchangers generally, many existing kitchens fail to incorporate any kind of heat exchanger due to integration costs. Retrofitting existing kitchen equipment with heat exchanger systems may require an entirely new flue hood assembly and substantial piping and accessories. This conversion is both time consuming and expensive. While some improvements have been made to combine a filter and heat exchanger, such as in U.S. Pat. No. 5,456,244, there remains room for improvement in the art. For instance, there is a desire for a filter unit having a simplified construction that uses less material and achieves greater heat transfer rates than prior devices.